The present invention relates to a print wheel and a method of automatically identifying various print wheels in a printing mechanism of a typewriter or other office machine of similar construction. In particular, the present invention relates to a method of identifying an improved print wheel of the type comprising a hub having a centrally disposed bearing bore, and a plurality of spokes extending radially from the hub with each spoke carrying a type face at its outer end, and with the hub having one element of a pin/slot connection from coupling the hub in a form-locking manner with a print wheel receptacle, which is driven by a drive motor, of a print mechanism to fix a defined angle between the drive motor and a zero position of the print wheel.
Presently employed printers, such as widely used serial printers, use a large number of print wheels bearing different type faces corresponding to various languages and fonts, and a considerable number of different print wheels exist for various printing purposes. Although these print wheels contain different type faces, they usually have the same overall structure so that they are easily interchangeable for use in different printers. These print wheels may also be rotatably arranged within cartridges which can then be interchangeably inserted for a specific printing process into a serially operating printer.
Although both the print wheels and their associated cartridges have the same structure, printing conditions differ depending on the type or consistency of a print wheel, so that, when print wheels are to be exchanged, operating conditions on the side of the printer itself must be changed to correspond to the exchange of print wheels. For example, the imprint strength, pitch, ribbon advance and/or other parameters of the printing mechanism may need adjustment when changing print wheels to obtain satisfactory printing.
U.S. Pat. No. 4,018,639 to Staples discloses a printing element in the form of a print wheel which is not provided with a code or a display that is machine readable. Thus, a printing machine receiving a printing element according to this patent cannot automatically cause a printer to change operating conditions when new printing elements are encountered. Instead, the Staples print elements require an operator of the machine to identify information on the printing element and to appropriately set parameters of the printer for each printing element so identified.
Another known printing system is disclosed in U.S. Pat. No. 3,498,439 to Willcox and employs a coded disc in connection with type elements to automatically set the printer to operate in a certain manner. However, the type element does not bear a code.
DE-OS 2,834,662 discloses a print wheel including a coded region scannable by a sensor that is in communication with a control circuit. The sensor reads the coded region and the circuit controls the printing system according to the coded region read by the sensor. The coded region includes a series of open and closed digit positions which constitute a binary code. The first and second digits are always open providing an unequivocal starting or rest position. The third digit is coded to indicate whether this is a regular or a special printing element. The fourth, fifth and sixth digits following the third digit are coded to provide information for controlling the spacing or pitch between type faces. The seventh digit is coded to indicate the number of type faces and the eights and ninth digits to indicate the striking force of the hammer. The drawback of this solution is the relatively high manufacturing costs involved in the application of the extensive coded region on individual print wheels and for the additional sensor device.